Method for communicating in a mobile network

ABSTRACT

The present invention relates to a method for communicating between a primary station and at least one secondary station, comprising
         (a) the secondary station being configured to search a first configuration of search spaces, said search spaces comprising a number of resource sets, where at least one resource set might be used to transmit a message to the secondary station,   (b) configuring the secondary station by means of a configuration message to search a second configuration of search spaces,   (c) the secondary station in response of the reception of the configuration message entering into a transitional configuration mode, wherein the secondary station searches partly the first configuration of search spaces and the second configuration of search spaces.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application claims the benefit or priority of and describesrelationships between the following applications: wherein thisapplication is a continuation of U.S. patent application Ser. No.15/242,912, filed Aug. 22, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/635,689, filed Sep. 18, 2012, now U.S. Pat. No.9,426,671, issued on Aug. 23, 2016, which is the National Stage ofInternational Application No. PCT/IB2011/051376, filed Mar. 31, 2011,which claims the priority of foreign applications EP10305357.5 filedApr. 7, 2010 and EP10305456.5, filed Apr. 29, 2010, all of which areincorporated herein in whole by reference.

FIELD OF THE INVENTION

The present invention relates to a method for communicating in anetwork. More specifically, the present invention relates tocommunication between a primary station and a secondary station, in atelecommunication network, like a cellular telecommunication network(e.g. UMTS, GSM).

BACKGROUND OF THE INVENTION

In UMTS LTE the downlink control channel PDCCH (Physical DownlinkControl Channel) carries information such as resource allocation foruplink or downlink transmission. A PDCCH message can use 1, 2, 4 or 8Channel Control Elements (CCEs or resource elements)—referred to as CCEaggregation levels 1, 2, 4 or 8. PDCCH messages can be transmitted usingone of a set of available message formats (e.g. with different signalcharacteristics such as number of information bits and channel codingrate, The different formats are referred to in the LTE specifications as“DCI formats”. In addition, different destinations or purposes for thePDCCH messages may be indicated by different scrambling sequencesapplied to the message CRC (in the LTE specifications the differentscrambling sequences correspond to different identities, referred to asRNTIs). Different RNTIs are used to distinguish UE-specific PDCCHmessages intended for a particular UE, from Common PDCCH messagesintended for reception by more than one UE. In the case of a PDCCHmessage intended for reception by more than one UE, this could be for adefined group of UEs, or any UE.

A mobile station, like a UE in LTE, does not know in advance thelocation in CCE space of messages intended for it. In principle, themobile station could attempt to blindly decode all the possible PDCCHswith different starting positions in the CCE space and thus receive anymessages intended for that mobile station. However, if the CCE space islarge the processing complexity is prohibitive. Therefore a more limitedsearch is configured which consists of a number of search spaces. A UEmay search a given search space for messages with one of more DCIformats. For simplicity of explanation, we may consider only one DCIformat and one RNTI in a UE-specific search space, but the samediscussion is applicable for multiple DCI formats, multiple RNTIs andfor UE-specific and Common search spaces.

A search space is a set of aggregated CCEs (with a certain aggregationlevel) within which a mobile station (or user equipment (UE) orsecondary station) performs blind decoding of all PDCCH payloads (DCIformats and RNTIs) that it assumes may be transmitted for thataggregation level. The set of PDCCH payloads that the UE assumes may betransmitted may be a subset of all possible PDCCH payloads defined bythe LTE specification. Search spaces are defined per aggregation level;a secondary station thus can have up to four search spaces. For example,the search space of a UE for aggregation level 1 (referred to as 1-CCE)could consist of the CCEs indexed 3, 4, 5, 6, 7, 8, while its searchspace for aggregation level 8 could consist of the two resource sets ofaggregated CCEs consisting of the CCEs indexed by 1, 2, . . . 8 and 9,10, . . . , 16, respectively. In this example, the UE thus performs sixblind decodings for 1-CCEs and two blind decodings for 8-CCEs.

The LTE specification currently requires the UE to perform the followingin the search spaces designed for UE-specific PDCCH messages on a singlecarrier (i.e. UE-specific search space (UESSS)):

6 decoding attempts of 1-CCE aggregation

6 decoding attempts of 2-CCE aggregation

2 decoding attempts of 4-CCE aggregation

2 decoding attempts of 8-CCE aggregation

In addition the UE is required to perform the following in a searchspace designed for Common PDCCH messages on a single carrier (i.e.Common search space):

4 decoding attempts of 4-CCE aggregation

2 decoding attempts of 8-CCE aggregation

In a conventional wireless system represented on FIG. 1, a primarystation 100 exchanges data with a plurality of secondary stations 110.To transmit its data, the primary station 100 transmits sends its dataon a downlink data channel 101. This downlink data channel may beadjusted over time in response to several criteria, e.g. Quality ofService, interference, downlink channel quality. To inform the secondarystations 110 of these changes, the primary station 100 transmits controldata (or signalling) to the secondary stations 110 on a downlink controlchannel 102. Similarly, the secondary stations 110 transmit their dataon an uplink control channel 111. Moreover, an uplink control channel112 is used by the secondary station to request resources fortransmissions and/or for providing the primary station with feedback onthe downlink transmissions or on the channel quality state.

In many wireless systems, like mobile communication systems as UMTS LTE(Long Term Evolution), or LTE Advanced, signalling on control channels102 or 112 is provided so that it indicates the particulartime-frequency transmission resources to which the data is mapped on thedata channels 101 or 111, and the transmission scheme used for that data(i.e. the format/mode in which the data itself is transmitted). Inaddition the secondary station may provide channel state feedbackintended to assist the primary station in scheduling transmission tosuitable secondary stations using appropriate transmission resources andtransmission scheme. Therefore, in general a transmission mode may bedefined by one or both of a transmission scheme used by the primarystation or the type of feedback provided by the secondary station.

For UMTS LTE downlink communication, the relevant downlink controlchannel 101 that includes resource allocation and transmission formatinformation is known as Physical Downlink Control Channel (PDCCH). Themessage a PDCCH carries is known as Downlink Control Channel Information(DCI). The resource allocations for different transmission modes aretypically indicated using different DCI formats. The secondary station(here a User Equipment or UE) is configured to receive a limited numberof different DCI formats from the possible set. Therefore configuringthe types of DCI format expected by the UE in the PDCCH directlycontrols the transmission modes which may be expected by the secondarystation, and a particular transmission mode is signalled by theparticular DCI format used for resource allocation. The DCI Formatcontents can also be associated with a transmission mode (e.g. in LTE a1 bit field indicated uplink or downlink resources).

The following PDCCH properties may be configured/reconfigured at thesecondary station by higher layer signalling from the primary station:—

-   -   DCI formats (depending on transmission mode)    -   DCI format size (e.g. addition/removal of CIF field)    -   PDCCH Search spaces    -   Carriers (additional CCs for carrier aggregation, anchor        carrier, or handover).

However, because of the delays inherent in higher layer (RRC) signallingthe primary station does not know exactly when the secondary stationapplies the new configuration. Therefore, there is a possibility that aPDCCH message (e.g. with a particular new DCI format) may be transmittedby the eNB, but not received by the UE (either because it has not yetapplied the reconfiguration). Similarly PDCCH messages may be lost ifthe new configuration is applied earlier than expected by the eNB.

SUMMARY OF THE INVENTION

It is an object of the invention to propose a method of communicationwhich alleviates the above mentioned problem.

It is another object of the invention to provide a method enabling thesecondary station to receive DCIs, even though a request for a change offormat has been received.

It is another object of the invention to avoid losing PDCCH messages(particularly those indicating RRC signalling messages) withoutincreasing complexity (e.g. number of blind decodings).

To this end, in accordance with the invention, a method is proposed forcommunicating between a primary station and at least one secondarystation, comprising

(a) the secondary station being configured to search a firstconfiguration of search spaces, said search spaces comprising a numberof resource sets, where at least one resource set might be used totransmit a message to the secondary station,

(b) configuring the secondary station by means of a configurationmessage to search a second configuration of search spaces,

(c) the secondary station in response of the reception of theconfiguration message entering into a transitional configuration mode,wherein the secondary station searches partly the first configuration ofsearch spaces and the second configuration of search spaces.

The present invention also relates to a secondary station comprisingmeans for communicating with a primary station, the secondary stationbeing configured to search a first configuration of search spaces, saidsearch spaces comprising a number of resource sets, where at least oneresource set might be used to transmit a message to the secondarystation,

-   -   a receiver for receiving a configuration message for configuring        the secondary station to search a second configuration of search        spaces,

control means for configuring the secondary station in response to thereception of the configuration message to enter into a transitionalconfiguration mode, wherein the secondary station searches partly thefirst configuration of each spaces and the second configuration ofsearch spaces.

In accordance with still another aspect of the invention, a primarystation is proposed, the primary station comprising means forimplementing a method in accordance with the first aspect of theinvention.

These and other aspects of the invention will be apparent from and willbe elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way ofexample, with reference to the accompanying drawing, wherein:

FIG. 1 is a block diagram of a system in accordance with the inventioncomprising a primary station and at least a secondary station.

FIG. 2 is a time chart representing schematically a PDCCH in a firstembodiment of the invention.

FIG. 3 is a time chart representing schematically a PDCCH in a secondembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for communicating in anetwork, like a cellular network. For instance, the network may be aUMTS network as depicted on FIG. 1.

Referring to FIG. 1, a radio communication system in accordance with theinvention comprises a primary station (BS or eNodeB) 100 and a pluralityof secondary stations (MS or UE) 110. The primary station 100 comprisesa microcontroller (μC) 102, transceiver means (Tx/Rx) 104 connected toantenna means 106, power control means (PC) 107 for altering thetransmitted power level, and connection means 108 for connection to thePSTN or other suitable network. Each UE 110 comprises a microcontroller(μC) 112, transceiver means (Tx/Rx) 114 connected to antenna means 116,and power control means (PC) 118 for altering the transmitted powerlevel. Communication from primary station 100 to mobile station 110takes place on downlink channels, while communication from secondarystation 110 to primary station 100 takes place on uplink channels. Inthis example, the downlink channels comprise control channels, likePDCCH. Such control channels may be transmitted over a plurality ofcarriers. These carriers may be defined by frequency carriers or in avariant of the invention, coding modulation.

In such a system, the DCIs may have a plurality of formats, eachdedicated to one transmission mode.

The Physical Downlink Control Channel (PDCCH) serves a variety ofpurposes. Primarily, it is used to convey the scheduling decisions toindividual UEs, i.e. scheduling assignments for uplink and downlink. ThePDCCH is located in the first OFDM symbols of a subframe. For framestructure type 2, PDCCH can also be mapped onto the first two OFDMsymbols of DwPTS field. An additional Physical Control Format IndicatorChannel (PCFICH) carried on specific resource elements in the first OFDMsymbol of the subframe is used to indicate the number of OFDM symbolsfor the PDCCH (1, 2, 3, or 4 symbols are possible). PCFICH is neededbecause the load on PDCCH can vary, depending on the number of users ina cell and the signaling formats conveyed on PDCCH.

As explained above, the information carried on PDCCH is referred to asdownlink control information, or DCI. Depending on the purpose of thecontrol message, different formats of DCI are defined. As an example,the contents of DCI format 1 are shown in the Table 1 below as anexample. DCI format 1 is used for the assignment of a downlink sharedchannel resource when no spatial multiplexing is used (i.e. thescheduling information is provided for one code word only). Theinformation provided contains everything what is necessary for the UE tobe able to identify the resources where to receive the PDSCH in thatsubframe and how to decode it. Besides the resource block assignment,this also includes information on the modulation and coding scheme andon the hybrid ARQ protocol.

TABLE 1 Contents of DCI format 1 carried on PDCCH Information typeNumber of bits on PDCCH Purpose Resource allocation header 1 Indicateswhether resource allocation type 0 or 1 is used Resource blockassignment Depending on resource Indicates resource blocks to allocationtype be assigned to the UE Modulation and coding 5 Indicates modulationscheme scheme and, together with the number of allocated physicalresource blocks, the transport block size HARQ process number 3 (TDD), 4(FDD) Identifies the HARQ process the packet is associated With New dataindicator 1 Indicates whether the packet is a new transmission or aretransmission Redundancy version 2 Identifies the redundancy versionused for coding the packet TPC command for PUCCH 2 Transmit powercontrol (TPC) command for adapting the transmit power on the PhysicalUplink Control Channel (PUCCH) Downlink assignment index 2 number ofdownlink (TDD only) subframes for uplink ACK/NACK bundling

The Cyclic Redundancy Check (CRC) of the DCI is scrambled with the UEidentity that is used to address the scheduled message to the UE.

For each transmission mode corresponds a DCI format. For example, DCIformat 1A is used for compact signalling of resource assignment ofsingle codeword PDSCH transmissions. DCI format 1B is used for compactsignalling of resource assignment of PDSCH transmissions using closedloop precoding with rank 1 transmission. Similarly there is DCI format1D for MU-MIMO transmission on the PSDCH. The exhaustive list of DCIformats is omitted for the sake of conciseness.

DCI (Downlink Control Information) format 0 is used on PDCCH to conveythe uplink scheduling grant, is shown in table 2 below.

TABLE 2 Contents of DCI format 0 Information type Number of bits onPDCCH Purpose Flag for format 0/format1A 1 Indicates DCI format to UEdifferentiation Hopping flag 1 Indicates whether uplink frequencyhopping is used or not Resource block assignment Depending on resourceIndicates whether to use type and hopping resource allocation type 1 ortype 2 frequency allocation hopping and index of starting resource blockof uplink resource allocation as well as number of contiguouslyallocated resource blocks Modulation and coding 5 Indicates modulationscheme scheme and redundancy and, together with the version number ofallocated physical resource blocks, the transport block size. Indicatesredundancy version to use New data indicator 1 Indicates whether a newtransmission shall be sent TPC command for scheduled 2 Transmit powercontrol PUSCH (TPC) command for adapting the transmit power on thePhysical Uplink Shared Channel (PUSCH) Cyclic shift for demodulation 3Indicates the cyclic shift to reference signal use for deriving theuplink demodulation reference signal from the base sequence Uplink index(TDD only) 2 Indicates the uplink subframe where the scheduling granthas to be applied CQI request 1 Requests the UE to send a channelquality indication (CQI)

In accordance with the embodiments of the invention, it is recognisedthat during the reconfiguration process it may be acceptable to losesome flexibility in scheduling in order that the primary station (oreNB) and the secondary station (or UE) can reliably communicate. Inaccordance with a current definition of the invention, this requiresthat the UE should be able to receive PDCCH messages according to bothold and new configurations, but with some loss in flexibility. Twoparticular embodiments are considered: Reducing the effective size ofthe search space for each configuration and reducing the fraction oftime for which each configuration is available.

(1) If the use of a new DCI format (or change in CIF (CIF is CarrierIndicator Flag (A 3 bit indicator of which carrier the is meant for thegranted resource signalled in the DCI))) is configured to replace anexisting DCI format then the UE specific search space is split so thatsome of the search space is allocated for the old DCI format and some ofthe search space is allocated to the new DCI format (e.g. the first halfof the search space for the old and second the half for the new). Thewhole of the search space is used for the new DCI format when thereconfiguration is confirmed or after expiration of a timer. This firstembodiment is shown on FIG. 2 for example described hereafter.

(2) Alternatively, UE specific search space is reserved for the old DCIformat on some subframes, and reserved for the new DCI format in othersubframes (e.g. odd subframes for the old, and even subframes for thenew). All subframes are used for the new DCI format when thereconfiguration is confirmed or after expiration of a timer. This secondembodiment is shown on FIG. 3 for example described hereafter.

With respect to the CIF, when cross carrier scheduling is configured,each grant will also contain this Carrier Indicator Flag (CIF) toindicate which carrier the grant applies to. The CIF field is added tothe existing Rel-8/Rel-9 DCI format (and new formats introduced inRel-10). In general, per carrier scheduling has the followingadvantages: a) allows different DCI formats to the same UE on differentcomponent carriers; and b) facilitates dynamic load balancing among thecomponent carriers on a sub-frame basis.

These two solutions ((1) and (2) above) enable the eNB to continue touse the old configuration for important data such as RRC messages (untilthe new configuration is confirmed or until a timer expired), but canswitch to using the new configuration for user data when appropriate. Ifsome user date is lost, this can typically be recovered by other meansif necessary.

The first and second embodiments (1) and (2) can be applied if theUE-specific search space itself changed (e.g. to accommodate schedulingon new carriers). In the first embodiment, this would mean that the UEsearches part of the old search space and part of the new search space.These two parts could be preconfigured or signalled when the new DCIformat is signalled. In the second embodiment, this would mean that theold search space is used in some subframes and the new search space isused in other subframes.

It is to be noted that the first and second embodiments (1) and (2) canas well be applied if the carrier on which PDCCH is to be monitored ischanged (e.g. handover, change of anchor carrier). For example, thefirst embodiment can be used provided it is within the UE capability tomonitor PDCCH on two carriers at the same time. The second embodimentwould require monitoring PDCCH on different carriers in differentsubframes.

In an example of these embodiments is a system like LTE-A. When areconfiguration occurs which would affect the DCI format used for RRCmessages (e.g. adding removing a CIF field), the UE enters into atransitional phase during which it uses partly the old format and thenew format. This partition can be one of the above explained embodiments(1) or (2). The amount of search space or which subframes are used forold and new DCI formats is predetermined. This could be by signalling orfixed by specification. The new configuration is fully applied when thereconfiguration is confirmed (e.g. by RRC signalling). In a variant, thenew configuration is fully applied after expiration of a timer. Thetimer duration may be set by signalling or fixed by specification.

In a variant, the transitional state of the secondary station where itmonitors partly the old configuration expires as soon as a message isreceived in accordance with the new configuration. Indeed, thisreception would mean that the primary station has also entered in thetransitional configuration mode, and thus, the secondary station may notneed to waste resources or energy in decoding the old configurationmessages. The primary station may continue to transmit in this mode fora predetermined duration if the secondary station does not signal thatit has switched to the new configuration mode.

As can be seen on the example of FIG. 2, for a considered secondarystation, the search spaces 201 in the first configuration mode I are forexample on a first set of carriers 210, although the search spaces 202on a second set of carriers 220 for the second configuration mode II.For the sake of clarity of representations, the difference between thetwo modes is in the sets of carriers. However, these embodiments are notlimited to this kind of difference which could be any of thoseparameters defining the formats. During the transitional configurationphase TP, starting with the reception of a configuration message, thesecondary station searches on a portion 201′ of the search spaces 201 oncarriers 210 and on a portion 202′ of the search spaces 202simultaneously, i.e. during the same subframe SF. These portions may bea subset of the subspaces that are searched in the normal configurationmode as illustrated. But these may as well be portions of thesesubspaces. Moreover, it can happen, depending on the situation of theportions of search spaces, that the secondary station listens to bothsets of carriers 210 and 220 at the same time. When the transitionalconfiguration phase TP expires, for example after a predeterminedduration or after the reception of a message in the second configurationsearch spaces, the secondary station listens to all the search spaces ofthe second configuration. It is to be noted that in this example thesecondary station only listens to a portion of the second configurationsearch spaces in the TP. However, in a variant of this embodiment, itcan listen partly to the first configuration search spaces and to thewhole set of search spaces of the second configuration.

An example of the second embodiment is described on FIG. 3. As can beseen on the example of FIG. 3, for a considered secondary station, thesearch spaces 301 in the first configuration mode I are for example on afirst set of carriers 310, although the search spaces 302 on a secondset of carriers 320 for the second configuration mode H. During thetransitional configuration phase TP, starting with the reception of aconfiguration message, the secondary station searches the search spaces301′ on carriers 310 in some subframes and the search spaces 302′ duringthe remaining subframes. Thus, in this particular example, the secondarystation listens to only one set of carriers 210 and 220 at the sametime, or even in the same subframe. This transitional configuration modemay then be preferred for secondary stations not being able to listen toso many carriers at the same time. When the transitional configurationphase TP expires, for example after a predetermined duration or afterthe reception of a message in the second configuration search spaces,the secondary station listens to all the search spaces of the secondconfiguration. It is to be noted that in this example the secondarystation only listens to the second configuration search spaces in somesubframes, e.g. the odd numbered subframes of the TP. However, in avariant of this embodiment, it can listen to the first configurationsearch spaces in some subframes only and to the whole set of searchspaces of the second configuration in every subframe of the TP.

Until the reconfiguration is completed the primary station can send aPDCCH message according to the old format in the appropriate part of thesearch space or appropriate subframe. The primary station may thus sendthe signal twice during the TP, once in the first configuration part ofthe TP and once in the second configuration part of the TP.

Further variations of the above embodiments are possible. In thesevariants, the primary station initiates the reconfiguration by thetransmission of a RRCConnectionReconfiguration message via RRCsignalling (or other higher signalling). On reception of this message,and once the secondary station has completed the reconfiguration, ittransmits to the primary station an RRCConnectionReconfigurationCompletemessage via higher layer signalling. If the primary station does notreceive the RRCConnectionReconfigurationComplete message,retransmissions of the RRCConnectionReconfiguration message may becarried out. Only on reception of thisRRCConnectionReconfigurationComplete message, is the primary stationsure that the secondary station has finished its reconfiguration.

In a first variant of these embodiments, one of the first or secondconfigurations of search spaces comprises that no CIF is provided forall DCI formats for same-carrier scheduling in UE-specific search space.The CIF is not attached for scheduling on the same carrier. Then, RRCsignalling can be handled even during CIF initialization/releaseprocedures. This option can be applied for all CCs or at least one CC.

In another variant of these embodiments, one of the first or secondconfigurations is that no CIF is attached for DCI format 0/1A forsame-carrier scheduling in UE-specific search space, although other DCIformats have CIF. In Rel-8, DCI formats 0/1A are defined for fallbackmode operations, and in the same manner, only DCI format 0/1A can beused during uncertain CIF initialization/release periods. The advantagecompared to the first variant is more possibility for BD (blinddecoding) reduction. For example, among two sets of DL and UL blinddecoding attempts, DL DCI formats with CIF can have a unified size withother DL DCI formats for cross-carrier scheduling, and this could helpto reduce the blind decoding attempts in the shared search space by K,where K is the number of PDCCH candidate positions in a given searchspace.

In accordance with a further variation of the above embodiments, it isproposed to delay the reconfiguration of CIF until after theRRCConnectionReconfigurationComplete message is transmitted by the UE.This allows a common understanding at the UE and eNB that the PDCCH withresource allocation for the RRCConnectionReconfigurationComplete message(and any retransmissions of the RRCConnectionReconfiguration message)will be transmitted without CIF. This has some possible disadvantageslike:

-   -   Additional delay in applying the reconfiguration;    -   Because of HARQ operation, there is some uncertainty on exactly        when the RRCConnectionReconfigurationComplete message will be        received by the eNB;    -   This violates the general 15 ms timing requirement for the UE to        implement reconfigurations.

In a similar variation of the above embodiments, it is possible to delaythe reconfiguration of CIF for Format 0/1A until after theRRCConnectionReconfigurationComplete message is transmitted by the UE.The reconfiguration for other DCI formats than Format 0/1A is availablewith no delay. In some cases there could be confusion in the UE-specificsearch space between Format 0/1A without CIF and other DCI formats withCIF having the same size. This has some possible disadvantage sincethere would potentially be ambiguity problems with DCI formats with CIFhaving the same size as DCI formats 0/1A without CIF (e.g. if CCs havedifferent bandwidths). To avoid ambiguity a scheduling restriction(during reconfiguration) or padding solution can be considered.

In accordance with a further variation of the above embodiments, it isproposed to apply the reconfiguration of CIF to some of the UE-specificsearch space immediately, but delay the reconfiguration of CIF for theremaining part of the search space until a DCI format is received withthe new value of CIF. This allows the resource allocation for theRRCConnectionReconfigurationComplete message (and any retransmissions ofthe RRCConnectionReconfiguration message) to be transmitted with orwithout CIF (in the appropriate part of the search space). It alsoallows cross-carrier scheduling according to the new configuration withminimal delay. This may under some conditions cause the following:

-   -   Some reduction in scheduling flexibility while the search space        is split.    -   Some uncertainty at the eNB on when the UE first correctly        receives a DCI format with the new value of CIF. However, the        eNB may continue using only part of the search space until it is        sure that the UE has applied the new configuration to the whole        search space.

In still another variant of the above embodiments, the secondary stationmonitors for DCI format 0/1A both with and without CIF (in UESSS) untilformat 0/1A is received with the new value of CIF. This allows theresource allocation for the RRCConnectionReconfigurationComplete message(and any retransmissions of the RRCConnectionReconfiguration message) tobe transmitted whether the eNB uses Format 0/1A with or without CIF.Minimal other specification changes would be needed. This solution hassome possible disadvantage: This solution implies additional blinddecodes for monitoring for both versions of Format 0/1A, but feweradditional blind decodes than would be required for monitoring for bothversions of all configured DCI formats. However, this additionalprocessing is likely to be within the capability of a UE supportingcarrier aggregation. However, if not, then the total number of blinddecodes could be maintained by restricting any scheduling using otherDCI formats for the newly configured carrier during the TP of thereconfiguration process.

In another variant of these embodiments, the secondary station monitorsfor DCI formats with and without CIF (in UESSS) in alternating subframesuntil a DCI format is received with the new value of CIF. This allowsthe resource allocation for the RRCConnectionReconfigurationCompletemessage (and any retransmissions of the RRCConnectionReconfigurationmessage) to be transmitted whether the eNB uses Format 0 with or withoutCIF. It also allows cross-carrier scheduling according to the newconfiguration with minimal delay. This latter solution may also resultunder some conditions in:

-   -   Some reduction in scheduling flexibility while using alternate        subframes.    -   Some uncertainty at the eNB on when the UE first correctly        receives a DCI format with the new value of CIF. However, the        eNB may continue using only every other subframe until it is        sure that the UE has applied the new configuration to all        subframes.

It is to be noted that the above embodiments could be applied together,and could be applied to the common search space (from the UE point ofview).

The invention may be applicable to mobile telecommunication systems likeUMTS LTE and UMTS LTE-Advanced, but also in some variants to anycommunication system having allocation of resources to be donedynamically or at least semi persistently.

In the present specification and claims the word “a” or “an” precedingan element does not exclude the presence of a plurality of suchelements. Further, the word “comprising” does not exclude the presenceof other elements or steps than those listed.

The inclusion of reference signs in parentheses in the claims isintended to aid understanding and is not intended to be limiting.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in the art of radiocommunication.

1. A primary station comprising means for communicating with at leastone secondary station, the primary station comprising: a transmitterincluding an antenna array arranged to communicate with the at least onesecondary station, a controller operative to configure the secondarystation to search a first configuration of search spaces, the firstconfiguration of search spaces comprising a first set of one or moreresource sets and a first set of one or more control message formats,where at least one resource set and control message format may beselected to transmit a control message to the primary station, atransmitter operative to transmit a configuration message requesting thesecondary station to search a second configuration of search spacescomprising a second set of one or more resource sets and a second set ofone or more control message formats, the controller operative toconfigure the primary station, after transmission of the configurationmessage, to enter into a transitional configuration mode, wherein theprimary station is configured to partly use the first configuration ofsearch spaces and to partly use the second configuration of searchspaces for transmitting a control message, wherein the secondconfiguration of search spaces comprises a second set of one or moreresource sets and a second set of one or more control message formats,wherein in the transitional configuration mode, the primary station isconfigured to search for a first control message format from the firstset of one or more control message formats in the first configuration ofsearch spaces and is further configured to search for a second controlmessage format from the second set of one or more control messageformats in the second configuration of search spaces, and wherein thefirst and second control message formats are different.
 2. The primarystation of claim 1, wherein the transitional mode is of a predeterminedduration.
 3. The primary station of claim 1, wherein the transitionalmode ends when the primary station finds a control message addressed tothe primary station in the second configuration of search spaces.
 4. Theprimary station of claim 1, wherein the transitional mode ends when theprimary station receives a message confirming the use of the secondconfiguration of search spaces.
 5. The primary station of claim 1,wherein the transitional mode comprises the primary station searchingthe first configuration of search spaces in a first subset of subframes.6. The primary station of claim 5, wherein the transitional mode furthercomprises the primary station searching the second configuration ofsearch spaces in a second subset of subframes not included in the firstsubset of subframes.
 7. The primary station of claim 1, wherein thetransitional mode comprises the primary station searching only a firstportion of search spaces of the first configuration of search spaces. 8.The primary station of claim 1, wherein the transitional mode furthercomprises the primary station searching only a second portion of searchspaces of the second configuration of search spaces.
 9. The primarystation of claim 8, wherein the transitional mode further comprises theprimary station searching only a second portion of search spaces of thesecond configuration of search spaces and wherein the first portion ofthe search spaces of the first configuration of search spaces does notoverlap the second portion of the search spaces of the secondconfiguration of search spaces.
 10. The primary station of claim 1,wherein the configuration message is transmitted by higher layersignaling.
 11. The primary station of claim 1, wherein the primarystation uses the second configuration partly in the transitional mode.12. The primary station of claim 13, wherein during the transitionalmode, a carrier indicator flag is used in accordance with the secondconfiguration of search spaces.
 13. The primary station of claim 1,wherein the transitional mode ends when an acknowledgement message istransmitted by a transmitter of the primary station, the acknowledgementmessage indicating an acknowledgement of at least one of: the receptionof the configuration message, and implementation of a reconfiguration.14. A computer readable storage medium that is not a transitorypropagating signal or wave, the medium having structures that encodeinstructions and when the structures are connected with processingcircuitry of a primary station, they control the primary station tooperates to: configure a secondary station to search a firstconfiguration of search spaces, the first configuration of search spacescomprising a first set of one or more resource sets and a first set ofone or more control message formats, where at least one resource set andcontrol message format may be selected to transmit a control message tothe secondary station, transmit a configuration message requesting thesecondary station to search a second configuration of search spacescomprising a second set of one or more resource sets and a second set ofone or more control message formats, configure the primary station,after transmission of the configuration message, to enter into atransitional configuration mode, wherein the primary station is adaptedto partly use the first configuration of search spaces and to partly usethe second configuration of search spaces for transmitting a controlmessage, wherein the second configuration of search spaces comprises asecond set of one or more resource sets and a second set of one or morecontrol message formats, wherein in the transitional configuration mode,the secondary station is configured to search for a first controlmessage format from the first set of one or more control message formatsin the first configuration of search spaces and is further configured tosearch for a second control message format from the second set of one ormore control message formats in the second configuration of searchspaces, and wherein the first and second control message formats aredifferent.